1. Field of the Invention
This invention relates to a double-faced vacuum fluorescent display in which luminescent display portions take place on both sides of an outer casing.
2. Description of the Related Art
A double-faced vacuum fluorescent display is currently known in which luminescent display portions are mounted on an outer casing at a base-plate side and a front-plate side facing the base-plate side, respectively, so that a luminescent material of these display portions can be observed from the front-plate side. This kind of double-faced vacuum fluorescent display is disclosed in, for example, Japanese Patent Publication No. SHO 56-11988. FIG. 25 of the accompanying drawings shows this double-faced vacuum fluorescent display. According to this publication, the combination of display patterns of the two luminescent display portions is exemplified by a combination of a digital display and an analog display, a combination of the digital or analog display and a special pattern display, and a combination of the digital display and digital display. In the combination of the two digital displays, character segments are mounted respectively on the front-plate side and the base-plate side and display so as not to overlap with each other in an effort to minimize interdigit spaces. This publication is totally silent about the kind of fluorescence.
The front plate of the double-faced vacuum fluorescent display of FIG. 25 has a flat-bottomed boat-shape molded front 1, and a wiring pattern 3 leading to the base-plate side 2 is formed on the inner surface of the molded front 1 by indium-tin oxide.
However, since the molded front 1 requires necessarily a mold, the prior display is expensive. Consequently an assembled front has been widely used recently in which frame-like side plates are combined with the front plate. With the assembled front, unlike the molded front, the wiring method was difficult to achieve. To this end, as disclosed in Japanese Patent Laid-Open Publication No. SHO 59-111239 and as shown in FIG. 26, wires lead to the front plate 4 and the base plate 5 and various external terminals 6, 7 are attached thereto.
In this prior double-faced vacuum fluorescence display, a frame-shape insulating film is formed over the outer peripheral portion of the front plate in order to secure insulation between the wires connected to the electrodes, etc. and shield external light. Also, on the base-plate side, an insulating film is formed under the display portion over the substantially entire surface.
As shown in FIGS. 27 and 28, a getter 9 is mounted in the outer casing of the prior double-faced vacuum fluorescent display. The getter is mounted on a non-illustrated spacer frame, which extends on and along the inner surface of the back base plate 10, via a support member 11. To this getter 9, electrodes of a high-frequency induction heater are brought closely from an outside of the outer casing 8 to radiate high frequency waves. As a getter container is heated, a getter material will be evaporated so that a getter film is formed over the inner surface (over the insulating film 13) of the front base plate 12 facing the getter 9.